A 17 year old girl suddenly holds her
chest and collapses to the ground
while playing volleyball at school.
A nurse who was present at the scene
rushes to evaluate the situation
and realizes that the girl has
no pulse and isn't breathing.
The nurse starts chest compressions immediately.
An automated external defibrillator(AED) is brought to
the scene within three minutes and a shock is delivered.
The girl regains consciousness
and a regular sinus rhythm.
She is rushed to the emergency department.
In the emergency department, her heart
rate is 65 beats per minute, it's regular
and her blood pressure is 122/77 mmHg.
EKG shows a shortened PR interval, a wide QRS
complex, a delta wave and an inverted T wave.
Which of the following is the most likely pathology
in the conduction system of this patient's heart?
Answer choice (A) - automatic discharge
of irregular impulses in the atria
(B) - impulse generation
by tissue in the AV node
(C) - Wandering atrial pacemaker
(D) - Accessory pathway
from atria to ventricles
or (E) blockage in the
Now take a second to come
to your own conclusion
Now let's discuss the question
Now looking at the subject, this patient
seems to have a cardiovascular concern
and they're telling us about ecg findings,
thus this is likely a cardiovascular question.
Now this question is a 2-step question which
means that we have to make one conclusion,
and then go one step deeper to
then find the correct solution
and the stem is required in this case.
We can't just read the last
sentence and know the answer,
we have to rely on the details
in the clinical vignette.
Now let's do our walkthrough.
the first thing we need to do is determine the
underlying characteristics at patient's presentation
Now the patient is young and
otherwise healthy as far as we know.
The main event that's described in the clinical vignette
is sudden loss of consciousness with immediate recovery
and she even has a normal pulse and normal
blood pressure right after recovery
but that's after delivery of defibrillator shock.
Now an abnormal ECG persist beyond recovery
and it includes a shortened PR interval,
a wide QRS complex and delta waves
which are abnormal upstrokes of the QRS
Now this suggests accelerated electrical
impulses from atria to ventricles.
Now, patient's presentation in this case can be summarized
as what's called an acute reversible arrythmic event.
Now this is in the context of what appears to be
an underlying electrical conduction abnormality
Now the second step we need to do is,
we need to figure out what type of electrical
conduction abnormality does this patient have?
Well, the EKG shows that the conduction abnormality
involves impulses between atria and ventricles
While the electrical conduction upstream
to the atria appears to be normal
There is no P wave abnormalities
but there is a short PR interval,
and that's when you have atrial depolarization to
the time of beginning ventricular depolarization.
Also, we have a wide QRS,which is when you have
complete depolarization of the ventricles
so that that means that there is some
type of abnormality
between the conduction times in which the
atria and the ventricles are involved.
Now, given the combination of reversibility
of arrythmia immediately after shock
and EKG findings discussed already,
this shows that the pathology here
is excessive electrical firing,
making an accessory pathway from
the atria to the ventricle,
the most likely etiology
here for this patient.
Now having an accessory pathway
from atria to ventricles
is the pathophysiology in a condition
known as Wolff-Parkinson-White syndrome
which is the most likely conduction
abnormality for this patient.
And thus the answer choice is (D) - accessory
pathway from the atria to the ventricles.
Now let's discuss some high-yield facts for this question.
Wolff-Parkinson-White Syndrome is a condition in which
there is electrical conduction abnormally in the heart
in which it uses an accessory pathway between the atria
and the ventricles that actually bypasses the AV node
Normally, electricity goes from the atria
to the ventricles through the AV node,
but in WPW or Wolff-Parkinson-White, we have an
accessory pathway that goes around the AV node
and goes quicker from the atria to the ventricle hence
the shortened PR interval in this patient's description.
Now, bypassing the AV node,
where in the AV node,
usually the impulse waits before
being propagated further,
conduction to the accessory pathway
travels at a significantly higher rate
than what we would normally expect.
When this conduction creates an electrical circuit or loop,
the result is supraventricular
tachycardia and accessory symptoms.
Now delta waves on EKG are pathognomonic
for WPW or Wolff-Parkinson-White.
Now athough most people with accessory
pathway never show symptoms.
WPW is one of the most common causes
of tachycardia in young patients.